I. Field of the Invention
This invention relates generally to manhole and catch basin structures and, more particularly, relates to a stackable plastic extension member positionable between the open top surface of a base of a manhole or catch basin and the bottom surface of a support frame. The extension may be used to elevate a manhole cover support frame or a catch basin grating support frame, wherein the central axis of the manhole cover support frame or catch basin grating support may be aligned either parallel to or at an angle relative to the vertical axis of the manhole or catch basin. The angle relative to the vertical axis of the manhole or catch basin may be compounded at a simple or complex angle by stacking a plurality of extensions. The plastic extension may include a combination of upward and downward facing pockets, whereby there is an increase in surface area of both portions of the extension ring that contact the top of the base of the manhole or catch basin and the bottom of the manhole cover support frame or catch basin grating support frame.
II. Discussion of the Prior Art
Roadways or streets often include manholes or catch basins, allowing access to underground sanitary and storm sewers and utility conduits. A manhole may generally comprise a base having concentric sides extending upward, a cone mounted above the base (usually of a monolithic, tubular, conical, or cylindrical cast made of concrete or brick), a cast iron support frame and a cover. The cast iron support frame is positioned above the cone and supports the cover. During roadway construction or resurfacing, the concrete manhole structure is built up to an elevation so that the cover will be positioned approximately flush with the road level. One or more concrete spacers may be positioned between the cast iron support frame and cone, to ensure that the cover will be flush with the road surface.
Catch basins are constructed along the curb line of roadways or streets to allow surface water drainage into underground storm sewers. The catch basin structure is similar to the manhole structure. The catch basin, when first constructed, comprises a base with concentric sides extending upward, a cone resting above the base with a rectangular, cylindrical, oblong, etc. cross-section on which is mounted a cast iron support frame having a rectangular opening that supports a rectangular grating. Sometimes, a rectangular top slab may be positioned directly above the cone. The rectangular top slab is used to narrow the opening in the cone and supports either a rectangular or concentric cast iron support frame. When the catch basin structure is built up to an elevation to ensure that the grating will be approximately at road level, rectangular spacers are employed between the cone or top slab and the cast iron support frame.
Occasionally, the manhole and catch basin are constructed on a hillside. Usually, the base of the manhole or catch basin is aligned vertically with the earth's gravitational line, not perpendicular to the surface or the hillside's vertical line. In order to avoid having a recess (pothole) in the roadway, the manhole cover or grating must be supported at an angle or slope relative to the base, wherein the slope is equal to the angle between the gravitational line and the hillside vertical line. To further complicate matters, the hillside may also be curved, creating a complex angle between the plane of the manhole cover and the vertical axis of the manhole base. Thus, a need exists to efficiently change the angle of the manhole cover and grating to be flush with the resurfaced roadway.
The prior art has recognized a need to efficiently raise the level of the manhole flush with the resurfaced roadway. To meet this need, a variety of adapter rings and adjustment rings have been introduced, such as that described in U.S. Pat. No. 5,470,172 (hereinafter the '172 patent) issued to Wiedrich. The '172 patent shows and describes an extension ring that is positioned between the upper surface of the monolithic cone and the bottom surface of the support frame casting. One embodiment of the extension ring described in the '172 patent includes downward facing pockets formed by inner and outer sidewalls and webs extending between the sidewalls. In use, it is difficult to fill the downward facing pockets with mortar or other similar filler. Also, wedges 11 are shown and described to engage with the webs, changing the slope of the planar support surface of the extension ring. The use of wedges may not allow the user to easily create a desired complex slope angle. The use of wedges also requires additional steps of alignment and positioning. Further, all the weight/force is localized on the webs and outer wall. Hence, a need exists for an extension member that spreads out the bearing weight over a substantial portion of the top surface of the cone, wherein the extension member may be used to easily create a desired complex slope angle. The present invention meets these and other needs.